Traditionally used surgiCal masks have been found to provide limited protection against airborne Mycobacterium tuberculosis and other infectious agents. More protective respirators, currently used in industrial settings, have been modified for use in health care, but have not been studied for their effectiveness against pathogens. It is proposed to develop new methods for determining the bacterial penetration, injury, survival and aerosolization-after-storage characteristics of currently used and potential respiratory protection devices. Mycobacterium bovis BCG vaccine strain and other representative strains will be used as models in the tests. The airborne microorganisms will be studied by microbiological and physical means. A new aerodynamic particle sizing instrument will measure the health-significant aerodynamic particle size of the microorganisms down to 0.3 microm. An optical size spectrometer will detect the fragments below 0.3 microm from the deposited, potentially injured microorganisms. New bioaerosol samplers, developed by the investigators, and different growth media will be used to measure the concentration levels, injury and survival of the model microorganisms downstream of the respirators during tests simulating initial wear and tests on the degree of aerosolization after storage. These and other new methods will be used to study several respirators. Respirators with high versus low electrical charge levels embedded in them will be studied as to their bacterial penetration. The findings with the model microorganisms will be compared with results and analyses from tests with non-biological, spherical reference aerosols, performed in a previously developed respirator test facility. Since highly protective respiratory devices are more expensive than traditionally used ones, the studies will be performed on off-the-shelf respirators and on respirators stored after exposure to airborne microorganisms, typical of a day's activity. The levels of bacterial aerosolization after storage, measured downstream of the respirators, will be related to the material parameters of the respirators. Comparisons between the count from the microbiological analysis to the physical count of the test aerosol will assist the study of bacterial injury and survivability. The new methods and scientific data will be evaluated as to their potential use in future standards for certification and quality assurance testing of respirators used against airborne pathogens.